1. Field of the Invention
The present invention relates to machine tools, particularly a machine tool driven according to a numerical control (NC) program.
2. Description of the Background Art
A machine tool that rotatably drives an object of control such as a spindle, and that moves linearly an object of control such as a feed rod, according to an NC program, is known.
Japanese Patent Laying-Open No. 2000-317772 discloses a control method of such machine tools directed to reducing the cycle time. This method controls the machine tool such that machining of a workpiece is started after confirming that the spindle has reached a rotational speed designated by a data block in an NC program. This control method includes a first positioning step, a second positioning step, and a machining step.
In the first positioning step, the spindle having a tool attached is rotatably actuated and the feed rod is driven, allowing the tool to be positioned towards an index position for alignment of the machining site of a workpiece and the cutting direction. In the second positioning step, following confirmation of completion of the feed rod travel in the first positioning step, the tool is positioned in the cutting direction towards the machining start position without confirming arrival of the spindle at the designated rotational speed. In the machining step, following confirmation of completion of the second positioning step, arrival of the spindle at the designated rotational speed is confirmed. Then, the tool is delivered for machining in the cutting direction after confirming the arrival at the required speed.